Ruling Could Take Effect Immediately; State Attorney General Files for Stay and Appeal

DETROIT—A federal judge on Friday struck down Michigan's decade-old constitutional amendment that prohibited same-sex marriage, calling it a violation of the equal-protection clause of the U.S. Constitution.

"Many Michigan residents have religious convictions whose principles govern the conduct of their daily lives and inform their own viewpoints about marriage," U.S. District Judge Bernard Friedman wrote in his decision....